This invention relates to prevention against the spread of a fire suitable for an electric system and, more particularly, to an electric system equipped with safety device against the spread of a fire occurred in a housing where electronic components are accommodated.
An electronic system is a combination of electric components. The electric components such as, for example, monolithic integrated circuit devices are mounted on the circuit boards, and the circuit boards are usually accommodated in a case. The electric components, circuit boards and the case are usually made of incombustible material recommended in UL (Underwriters Laboratories inc.) standards. When a fire breaks out inside the case, the incombustible material resists against the spread of the fire.
The electric components are exothermic, and raise the temperature inside the case. The high temperature ambience is causative of malfunction. If the electric components generate non-ignoreable amount of heat, a forced ventilation device such as a ventilation fan is required for the electric system. The ventilation fan is attached to the case, and forcibly evacuates the high-temperature air from the inside space to the environment.
However, the ventilation fan is undesirable from the viewpoint of the prevention against the spread of a fire, because fresh oxygen is forcibly supplied to the fire. Even though the incombustible material is used inside the case, the fresh oxygen promotes the fire, and the fire is spread from the case to the outside. When the fire breaks out at a component in a lower portion inside the case, the fire is easily spread toward components in a higher portion inside the case. If a fire-protection shutter is provided inside the case, the fire-protection shutter prevents the components in the higher portion from the fire. However, the fire-protection shutter mechanism and the actuator for it are costly.
It is therefore an important object of the present invention to provide a safety device against a fire, which is economical and effective against a fire breaking out inside a case equipped with a ventilation device.
To accomplish the object, the present invention proposes to interrupt the air flow by using foam produced from a piece of foamable substance.
In accordance with one aspect of the present invention, there is provided an electric system comprising a case formed with at least one ventilation hole open to an inner space defined therein and an environmental space outside thereof and accommodating at least one exothermic electric component, and at least one piece of foamable substance provided on a surface of the case around the at least one ventilation hole and producing foam for reducing an open area of the aforesaid at least one ventilation hole when fire heats the piece of formable substance.
In accordance with another aspect of the present invention, there is provided an electric system comprising a case formed with at least one ventilation hole open to a first inner space defined therein and an environmental space outside thereof, at least one circuit board box accommodated in the inner space and having at least one circuit board where at least one exothermic electric component is mounted and a casing retaining the aforesaid at least one circuit board in a second inner space defined therein and formed with at least one air passage open to both of the first and second inner spaces, a ventilation device attached to the case and forcibly supplying the air from the environmental space through the first inner space to the second inner space for removing heat from the aforesaid at least one exothermic electric component, and at least one foamable panel partitioning the first inner space into a first inner sub-space connected through the aforesaid at least one ventilation hole to the environmental space and a second sub-space where the aforesaid at least one circuit board box is located and having a base plate formed with at least one hole open to the first and second sub-spaces and a piece of foamable substance provided on a surface of the base plate around the aforesaid at least one hole and producing foam for closing the aforesaid at least one hole when fire heats the piece.
In accordance with yet another aspect of the present invention, there is provided an electric system comprising a case formed with at least one ventilation hole open to an inner space defined therein and an environmental space outside thereof and having at least one circuit board where at least one exothermic electric component is mounted, a ventilation device attached to the case, and forcibly supplying the air from the environmental space to the inner space for removing heat from the aforesaid at least one exothermic electric component, and at least one foamable panel partitioning the inner space into a first inner sub-space connected through the aforesaid at least one ventilation hole to the environmental space and a second sub-space where the aforesaid at least one circuit board is located, and having a base plate formed with at least one hole open to the first and second sub-spaces and a piece of foamable substance provided on a surface of the base plate around the aforesaid at least one hole and producing foam for closing the aforesaid at least one hole when fire heats the piece.